Receptors, at the cell body of nerve cells, on binding of appropriate ligands, alter the rate of flow of specific inorganic ions through the cell membrane, and thereby determine whether a signal is transmitted to an adjacent cell. An understanding of the receptor-mediated processes on the molecular level and the ability to predict under what conditions a nerve cell will transmit a signal are the objectives of the investigations. Important to this objective is investigations of the relationship between the concentration of ligands and the rates with which a receptor allows a specific inorganic ions to move through the membrane. The rate constants for the movement of specific radioactive inorganic ions through a cell membrane will be investigated with membrane vesicles (microsacs) obtainned from the electric organ of Electrophorus electricus. These microsacs of about 3000 A diameter will allow rapid diffusion of specific inorganic ions through the membrane only in presence of acetylcholine-receptor ligands. Flow-quench methods with a time resolution of about 7 milliseconds will be used. Measurements of the rate constants for the opening of receptor-formed channels through the membrane (as indicated by changes in the transmembrane voltage) will be made. Voltage-sensitive dyes and a flash-isomerization method will be used to obtain a time resolution of approximately 10 microseconds. Kinetic and equilibrium measurements of the ligand binding will be made to investigate the relationship between the kinetics of inorganic ion fluxes and ligand binding. A fluorescent acetylcholine-receptor ligand, microsacs, and a stopped-flow apparatus will be used.